Hydrogen sulfide has rotten-egg-smelling odor that’s produced as organic materials decay. It is an extremely hazardous byproduct of industrial processes and it almost always occurs as a colorless gas, causing health problems and even death when inhaled, consumed, or in contact with skin.
Individuals have to be especially careful when working in spaces such as basements, manholes, sewers and manure pits because hydrogen sulfide is heavier than air, allowing it to travel across the ground and fill low-lying spaces.